The present invention relates to a reciprocating piston compressor, and in particular to a compressor wherein, in the event of abnormal compressor operating conditions, a pressure relief valve provides a leakage path between high and low pressure regions in the compressor.
More particularly, the present invention is applicable to a reciprocating piston compressor in which over-pressure conditions may occur in a cylinder head of the compressor during operation. In order to prevent damage to the compressor assembly, a pressure relief valve communicating with discharge pressures in the cylinder head is required. The pressure relief valve operates to vent excessive pressures in the cylinder head to a region of lower pressure, i.e., compressor suction pressure, when the discharge pressure reaches a predetermined differential value, with respect to the suction pressure, below that which would cause damage to the compressor assembly.
A typical prior art internal pressure relief valve used in a compressor assembly consists of a valve body encapsulating various valve components such as a valve seat, a ball, a piston, and a spring. The valve body includes a threaded portion that is assembled into the cylinder head by means of a threaded bore communicating directly with a discharge pressure chamber in the cylinder head.
There are several problems and disadvantages associated with using the aforementioned prior art pressure relief valve in a compressor assembly. For example, because the valve body extends outwardly from the cylinder head, space immediately surrounding the cylinder head is required, thereby leaving less room for other compressor components or resulting in a larger compressor. Also, some form of gasket is required to seal the valve in its mounted position to prevent unintended pressure leakage Furthermore, a tapped hole must be provided in the cylinder head to mount the valve.
Further considerations of manufacturability and cost make using the aforementioned pressure relief valve undesirable. For instance, when a used compressor is rebuilt or reconditioned, a new entire valve assembly must be used in order to ensure the integrity of its internal valve components. Also, during initial manufacturing of the compressor assembly, the pressure relief valve must be manufactured independently of the other compressor components and then assembled onto the cylinder head.